// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use crate::ast::Statement;
use crate::dialect::Dialect;
use crate::keywords::Keyword;
use crate::parser::{Parser, ParserError};

/// A [`Dialect`] for [SQLite](https://www.sqlite.org)
///
/// This dialect allows columns in a
/// [`CREATE TABLE`](https://sqlite.org/lang_createtable.html) statement with no
/// type specified, as in `CREATE TABLE t1 (a)`. In the AST, these columns will
/// have the data type [`Unspecified`](crate::ast::DataType::Unspecified).
#[derive(Debug)]
pub struct SQLiteDialect {}

impl Dialect for SQLiteDialect {
    // see https://www.sqlite.org/lang_keywords.html
    // parse `...`, [...] and "..." as identifier
    // TODO: support depending on the context tread '...' as identifier too.
    fn is_delimited_identifier_start(&self, ch: char) -> bool {
        ch == '`' || ch == '"' || ch == '['
    }

    fn identifier_quote_style(&self, _identifier: &str) -> Option<char> {
        Some('`')
    }

    fn is_identifier_start(&self, ch: char) -> bool {
        // See https://www.sqlite.org/draft/tokenreq.html
        ch.is_ascii_lowercase()
            || ch.is_ascii_uppercase()
            || ch == '_'
            || ch == '$'
            || ('\u{007f}'..='\u{ffff}').contains(&ch)
    }

    fn supports_filter_during_aggregation(&self) -> bool {
        true
    }

    fn supports_start_transaction_modifier(&self) -> bool {
        true
    }

    fn is_identifier_part(&self, ch: char) -> bool {
        self.is_identifier_start(ch) || ch.is_ascii_digit()
    }

    fn parse_statement(&self, parser: &mut Parser) -> Option<Result<Statement, ParserError>> {
        if parser.parse_keyword(Keyword::REPLACE) {
            parser.prev_token();
            Some(parser.parse_insert())
        } else {
            None
        }
    }

    fn supports_in_empty_list(&self) -> bool {
        true
    }
}
